azw3 to epub conversion stuck on 1%

Hi there,

I bought The Complete Works of Shakespeare from amazon. The azw3 file is about 4MB (5000+ printed pages). I have been unsuccessfully trying to convert it to epub, but the progress bar doesn't go beyond 1%. I am really puzzled, I have had no problems converting other kindle books of mine. I am on the latest version of Calibre 0.9.27, and running it on Mac OS 10.8

Any help much appreciated.

Thanks,
K.